In general, telecine machines that operate at 60 field/sec (actually, 59.94 fields/sec) employ a 3:2 pulldown convention to convert film media, which runs at 24 frame/sec (actually, 23.976/sec), to video media, which runs at 60 television field/sec (actually, 59.94 fields/sec). Specifically, a two-field video sequence and a three-field video sequence are alternately generated, with each field sequence corresponding to a film frame. These video fields are interlaced in that the film frames are scanned, such that alternating odd and even fields are generated, with the lines of the odd fields interleaved with the lines of the even fields. For example, a film frame can be scanned to generate a two-field video sequence characterized by an even field and then an odd field (even/odd). The next film frame can be scanned to generate a three-field video sequence characterized by an even field, then an odd field, and then an even field (even/odd/even). The respective first and second even fields in this three-field video sequence are duplicates. The next film frame can be scanned to generate a two-field video sequence characterized by an odd field and then an even field (odd/even). The next film frame can be scanned to generate a three-field video sequence characterized by an odd field, then an even field, and then an odd field (odd/even/odd). The respective first and second odd fields in this three-field video sequence are duplicates. This pattern then repeats for the next four film frames and so on.
The two/three-field video sequence is sometimes disrupted, such as, e.g., when the video is edited without regard to the video sequence. These disruptions in the video sequence can cause difficulties during processing that requires manipulation of the two/three-field sequence. For example, it is sometimes desired to convert 525 line, 60 fields/sec video to 625 line, 48 fields/sec video. During this procedure, the two/three-field video sequence is converted to a repeating two-field video sequence by removing the duplicate field from each of the three-field video sequences, and, if needed, swapping the order of the two-field video sequence, thereby generating a repeating two-field video sequence characterized by an even field and then an odd field through the entirety of the video (even/odd), or alternatively, an odd field and then an even field through the entirety of the video (odd/even). The 525 line resolution of the 525 line, 60 field/sec video is then interpolated to produce the 625 line, 48 field/sec video with 625 lines of resolution. The resulting 625 line, 48 field/sec video is recorded at 24 frames/sec, which is then played at 25 frames/sec, which is the normal 625 line, 50 field/sec video when viewed. When there is a disruption in the two/three-field video sequence prior to conversion, the two-field sequence subsequent to conversion will sometimes change dominance. That is, the repeating odd/even video sequence changes to a repeating even/odd video sequence. Because a television system cannot process an odd/odd video sequence (or an even/even video sequence), an even field (or odd field) by itself, or an even/odd/even video sequence (or an odd/even/odd video sequence) must be located at the change in dominance. As a result, the video is degraded.
Another example of a process that requires the manipulation of the two/three-field video sequence is the conversion of video to a digital video disk (DVD). To save memory, the two/three field video sequence is converted to a repeating two-field video sequence in much the same manner described above. The two-field video sequence is then compressed into a motion pictures expert group (MPEG2) format. The DVD player then restores the two/three-field video sequence during playback on the television system. Again, however, during conversion, the field dominance of the two-field video sequence may change, thereby degrading the DVD.
Thus, it would be desirable to provide methods and systems to correct a disrupted two/three-field video sequence.